The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Fuel and air injection quantities delivered to an engine are controlled to meet fuel economy requirements and emission standards. When fuel injectors function improperly, fuel injection quantities delivered to the engine may deviate from desired levels, resulting in increased emissions and/or decreased fuel economy.
Fuel injector diagnosis may be performed when the engine is shut off. The fuel quantity that flows through an injector may be estimated based on a fuel pressure at a common fuel rail before and after a fuel injection event. The estimated fuel quantity is compared with a desired fuel amount to determine whether the injector functions properly. When the engine is off, the measured fuel pressure is low and may be susceptible to errors due to pressure fluctuations following each fuel injection event. Generally, several fuel injection events are required on the same injector to ensure accurate measurement of the fuel pressure and accurate diagnosis of the injector.